Ecology: Community Structure, Food Webs, and Primary Production

What is a community?

A community is a group of interacting species that inhabit a common environment and interact with each other.

Define guild and functional group.

A guild is a group of species that exploit the same resources in a similar way, while a functional group is a collection of species that perform similar ecological roles or functions in an ecosystem.

What's the difference between a food web and an interaction web?

A food web illustrates the feeding relationships among species in an ecosystem, while an interaction web includes all types of interactions, such as competition and mutualism, not just feeding.

Distinguish between richness and diversity.

Richness refers to the number of different species in a community, while diversity takes into account both the number of species and their relative abundance, often quantified using indices like the Shannon index and Simpson's index.

What do rank abundance curves tell you about a community?

Rank abundance curves display the relative abundance of species in a community, illustrating species richness and evenness, which helps assess community structure.

What can we learn by comparing species accumulation curves from different locations or communities?

Comparing species accumulation curves can reveal patterns of biodiversity, species richness, and the rate of species discovery in different ecological contexts.

Define a trophic cascade.

A trophic cascade is an ecological phenomenon where changes in the population of one species (usually a predator) cause indirect effects on multiple other species in the food web.

Distinguish between direct and indirect interactions.

Direct interactions occur between two species that directly affect each other, while indirect interactions involve one species affecting another through a third species.

What is a trait-mediated indirect interaction?

A trait-mediated indirect interaction occurs when the traits of one species influence the behavior or population dynamics of another species through a third species.

What is the 'green world hypothesis'?

The green world hypothesis suggests that herbivores are limited by predators and other factors, allowing plants to thrive and maintain a green ecosystem.

Define trophic facilitation.

Trophic facilitation occurs when one species enhances the availability of resources for another species, often through indirect interactions.

Define keystone species.

A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance, playing a critical role in maintaining the structure of an ecological community.

Define foundation species.

Foundation species are species that have a strong role in structuring a community, often by providing habitat or resources for other species.

Define ecosystem engineer.

Ecosystem engineers are organisms that create, modify, or maintain habitats, significantly influencing the structure and dynamics of an ecosystem.

Explain what is meant by the 'context dependency' of an interaction.

The 'context dependency' of an interaction refers to the idea that the outcome of an ecological interaction can vary based on environmental conditions and the presence of other species.

Define primary succession.

Primary succession is the process of ecological change that occurs in an area where no soil exists, such as after a volcanic eruption or glacier retreat.

Define secondary succession.

Secondary succession is the process of ecological change that occurs in an area where a disturbance has destroyed an existing community but left the soil intact.

Define a climax community.

A climax community is a stable and mature ecological community that undergoes little change in species composition, typically established after a series of successional stages.

What are 'alternative stable states'?

Alternative stable states are different ecological states that a community can exist in, which can be stable under certain conditions, challenging traditional models of succession that suggest a single endpoint.

What is alpha diversity?

Alpha diversity refers to the diversity of species within a specific local area or habitat.

What is beta diversity?

Beta diversity measures the change in species composition between different habitats or ecosystems, reflecting the turnover of species.

What is gamma diversity?

Gamma diversity is the total species diversity in a larger region that encompasses multiple ecosystems or habitats.

What can we learn about local and regional processes by comparing local and regional diversity?

Comparing local and regional diversity helps us understand how local ecological factors and regional historical processes influence species richness and distribution.

What is vicariance?

Vicariance is the geographical separation of a population, typically due to a physical barrier, which can lead to speciation. It is relevant to continental drift as it explains how species distributions change over geological time.

What happened during the 'Great American Interchange'?

The Great American Interchange refers to the significant migration of species between North and South America that occurred when the Isthmus of Panama formed, allowing species from both continents to mix.

What are four hypotheses that explain the latitudinal gradient in species richness?

1. Climate stability hypothesis: warmer climates support more species. 2. Productivity hypothesis: higher productivity leads to more species. 3. Area hypothesis: larger areas support more species. 4. Historical hypothesis: longer evolutionary time allows for more speciation.

What is the species-area relationship?

The species-area relationship describes how the number of species increases with the area sampled. It is expected to differ between islands and mainlands due to factors like isolation and habitat diversity.

What are some explanations for the species-area relationship?

Explanations include the larger area providing more habitats and resources, lower extinction rates on larger islands, and the increased likelihood of species colonization.

What is the Equilibrium Theory of Island Biogeography (ETIB)?

The Equilibrium Theory of Island Biogeography posits that the number of species on an island is determined by the balance between immigration and extinction rates, influenced by island size and distance from the mainland.

What is the 'rescue effect'?

The rescue effect is a phenomenon where nearby populations can replenish or support a declining population on an island, reducing the risk of extinction.

What is the 'target effect'?

The target effect refers to the idea that larger islands have a higher probability of attracting new species due to their size and available resources.

What is meant by the idea that community membership is determined by 'a series of filters'?

This concept suggests that various environmental and biological factors act as filters that determine which species can successfully establish and persist in a community.

What do the warblers studied by Robert MacArthur illustrate about community structure?

MacArthur's study of warblers demonstrated that different species can coexist in the same habitat by utilizing different resources or niches, highlighting the importance of niche differentiation in community structure.

Explain the 'resource ratio hypothesis.'

The resource ratio hypothesis posits that the relative availability of resources, such as nutrients and light, determines which species can coexist in a community, influencing species diversity.

What is the 'paradox of the plankton'?

The paradox of the plankton refers to the observation that, despite the limited number of resources in aquatic environments, a high diversity of plankton species can coexist, challenging traditional ecological theories.

Explain the 'intermediate disturbance hypothesis.'

The intermediate disturbance hypothesis suggests that moderate levels of disturbance can enhance species diversity by preventing competitive exclusion, allowing both colonizers and competitors to coexist.

Explain the Menge-Sutherland model.

The Menge-Sutherland model describes how the interactions between species (such as competition and predation) and environmental factors influence community structure, particularly in rocky intertidal zones.

What is the Janzen-Connell hypothesis on seedling recruitment?

The Janzen-Connell hypothesis posits that seedling survival is higher away from parent trees due to reduced competition and herbivory, leading to higher diversity in plant communities.

Explain the 'lottery model.'

The lottery model suggests that species coexistence is determined by random events, where individuals of different species have equal chances of establishing in a community when resources become available.

Sketch and explain the three hypothetical ways in which species richness might be related to community function.

The three hypothetical relationships include: 1) Positive relationship - higher species richness leads to greater community function; 2) Saturation - community function levels off at high richness; 3) Negative relationship - too many species may lead to competition and reduced function.

What is gross primary production (GPP)?

Gross primary production (GPP) is the total amount of organic matter produced by photosynthesis in a given area and time, before any is used for respiration.

What is net primary production (NPP)?

Net primary production (NPP) is the amount of organic matter that remains after respiration by primary producers; it is the energy available for consumption by herbivores and decomposers.

What is the role of respiration in primary production?

Respiration in primary production refers to the process by which producers convert organic matter back into carbon dioxide and water, releasing energy for their own use and reducing the amount of energy available for growth and reproduction.

How does NPP vary with latitude?

NPP generally increases from the poles to the equator, with higher values in tropical regions due to warmer temperatures and higher precipitation.

How does NPP vary with global patterns in temperature and precipitation?

NPP is higher in areas with warm temperatures and abundant precipitation, as these conditions promote plant growth and photosynthesis.

How is NPP measured?

NPP can be measured using methods such as satellite imagery to assess vegetation cover, biomass sampling, and estimating carbon uptake through photosynthesis.

What is a trophic pyramid?

A trophic pyramid is a graphical representation of the distribution of biomass, energy, or numbers of organisms across different trophic levels in an ecosystem.

What is trophic efficiency?

Trophic efficiency is the percentage of energy transferred from one trophic level to the next, typically ranging from 5% to 20% due to energy loss at each level.

How can biomass pyramids be inverted in aquatic ecosystems?

In aquatic ecosystems, biomass pyramids can be inverted because primary producers (like phytoplankton) can have a lower biomass than the higher trophic levels (like zooplankton) due to rapid turnover rates.

What is secondary production?

Secondary production refers to the generation of biomass by heterotrophic organisms (consumers) through the consumption of primary producers and other organic matter.

How is the efficiency of secondary production related to heterotroph physiology?

The efficiency of secondary production is influenced by factors such as metabolic rates, digestive efficiency, and the energy content of the food consumed by heterotrophs.

What is the difference between bottom-up and top-down control of trophic cascades?

Bottom-up control refers to the influence of primary producers on the structure of the ecosystem, while top-down control refers to the impact of predators on lower trophic levels.

What are three factors that might affect the number of trophic levels in an ecosystem?

Three factors that can affect the number of trophic levels include the availability of energy (primary production), the size of the ecosystem, and the efficiency of energy transfer between levels.

What is meant by the background extinction rate?

The background extinction rate is the standard rate of extinction in Earth's biological history, typically measured in species per year, which serves as a baseline for comparing contemporary extinction rates.

How do contemporary rates of extinction compare to the long-term background rate?

Contemporary rates of extinction are significantly higher than the long-term background rate, often attributed to human activities such as habitat destruction, pollution, and climate change.

What is taxonomic homogenization?

Taxonomic homogenization refers to the process by which biodiversity is reduced and species composition becomes more similar across different geographic areas, often due to human influence.

List three threats to biodiversity and give a specific example of each.

1. Habitat destruction (e.g., deforestation for agriculture). 2. Pollution (e.g., plastic waste in oceans). 3. Climate change (e.g., rising temperatures affecting species distributions).